The subject matter disclosed herein relates to a ram air fan and, more particularly, to a ram air fan for surge bit detection.
An environmental control system (ECS) of an aircraft provides air supply, thermal control and cabin pressurization for the crew and passengers. Avionics cooling, smoke detection and fire suppression are also commonly considered part of an aircraft's environmental control system. At least a portion of the air supply for the ECS of a given aircraft is generated by the ram air inlet and the ram air fan (RAF). The ram air inlet is generally a small scoop located on a wing-to-body fairing and may include a modulating door to control an amount of cooling airflow through primary and secondary ram air heat exchangers as well as modulating vanes on ram air exhaust to increase ram air recovery. The RAF provides for ram air flow across the heat exchangers.
During operation, ram air is drawn through the heat exchangers by the RAF. However, it has been seen that contamination from ambient air flows will increase the pressure drop of the heat exchangers and may thereby reduce flow through the RAF and the heat exchangers. Indeed, significant heat exchanger contamination can reduce the airflow to the extent that the RAF can operate in an unstable operating mode (i.e., stall), which can cause excessive blade stress that may result in a failure of the RAF.